Generally, optical data transmission and optical storage systems require the use of current-input preamplifiers to condition the electrical signals received in the form of current pulses from input photodiodes. A commonly used topology for the preamplifier is the Trans-Impedance Amplifier (TIA) that converts the input current to voltage for the subsequent signal processing.
A conventional TIA 100 shown in FIG. 1 includes an amplifier 104 (e.g., an operational amplifier) having an inverting input (−), a non-inverting input (+), and an output. In the configuration shown, the non-inverting input (+) receives a biasing voltage. The inverting input (−) receives a current signal produced by a photo-detector 102 that is operated in a current sensing photoconductive mode. The output of the amplifier 104 is fed back to the inverting input (−) through a feedback resistor RF, thereby forming a voltage-current feedback network that senses the voltage at the output and returns a proportional current to the input. The −3 dB bandwidth is given by:f−3 dB=(½π)·ATIA/(RF·CD)                where                    RF is the feedback resistor,            CD is the photodiode capacitance, and            ATIA is the open-loop gain of the TIA.                        
With a TIA, such as the one shown in FIG. 1, there is a direct trade-off between the gain and the bandwidth, making it difficult to achieve both high-gain and wide bandwidth with a large photodiode capacitance. In addition, due to the finite bandwidth of the TIA, the input impedance Zin, which is equal to RF/ATIA, varies with frequency, making it behave like an inductance rather than a resistance. The resulting L-C tank at the TIA input may lead to gain peaking at high frequencies. In summary, disadvantages of the TIA approach include: strong process-dependency of gain setting due to the use of a feedback resistor as a gain element; limited input dynamic range for any fixed-gain setting; direct trade-off between the gain and the bandwidth; inherent gain peaking issues due to the inductive input impedance; and the need for a complex phase compensation network for variable gain settings.